Methods and apparatus for deposition of thin films

ABSTRACT

A method for depositing a thin film includes the steps of providing a vapor including at least one selected vapor phase component into an evacuated chamber and condensing the vapor onto a heated substrate to form a liquid phase deposit wherein a temperature of the substrate is lower than the condensation temperature of the component. The liquid deposit is then cooled to produce a solid phase film. The invention can provide two or more vapor phase components. The invention can be used to deposit a wide variety of layers, including thin films of metallic, semiconductor and nonmetallic inorganic materials. The invention is useful for forming solid electrolytes and the electrodes for batteries, fuel cells and other electromagnetically active devices.

CROSS REFERENCE TO RELATED APPLICATION

Not applicable.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

Not applicable.

FIELD OF THE INVENTION

The invention concerns methods and apparatus for depositing uniform thinfilms using vapor condensation.

BACKGROUND OF THE INVENTION

Thin films are important in the manufacture of electronic activedevices, such as microelectronics, batteries and fuel cells. In the caseof batteries, appropriate thin films can be used to form batterieshaving low internal series resistance, high capacity and other specificproperties required of modern batteries. However, despite continuingimprovements in thin film deposition methods, there has been limitedsuccess in the manufacture of thin (i.e., <10 μm) homogeneous films.Depending on the film material, available film deposition methods may beexpensive, provide an insufficient deposition rate or fail to providehomogeneous films.

A known vacuum method for the production of thin films is lasersputtering. However, this method is generally not suitable for theproduction of thin films for thickness below approximately 10 μm becauseof difficulties in achieving homogeneity and structural uniformity forthickness below this value.

Thin films used in batteries are commonly provided by vacuum depositionmethods. Other methods, such as mechanical or non-vacuum chemicaldeposition, can also provide thin films of various types, but thesefilms have certain properties rendering them generally unsuitable foruse in batteries or fuel cells. During these deposition process,substantial changes in the chemical or phase structure of the film canoccur, resulting in a film having properties which may differsignificantly from the initially deposited material. In most cases,these changes are unpredictable and adversely affect resulting filmproperties.

Different methods for the production of thin films for batteries havebeen developed. Most efforts have focused on attempts to develop thin,flat, small-area batteries, the batteries having low internal seriesresistance. Attempts to develop films for batteries having lowelectronic conductivity and high ionic conductivity have promptedresearch to develop suitable thin films for use as solid electrolytesand cathodes for high performance batteries, such as Li metal or lithiumion batteries. Solid electrolytes, as well as electrode materials,generally require a high degree of surface purity. In addition,batteries require good electrode/electrolyte contacts.

The above difficulties have been solved in part by a method disclosed byU.S. Pat. No. 6,132,653 to Hunt, et al. Hunt discloses an atmosphericmethod for chemical vapor deposition (CVD) using a very fine atomizationor vaporization of a reagent containing liquid or liquid-like fluid nearits supercritical temperature. The resulting atomized or vaporizedsolution is entered into a flame or a plasma torch, and a powder isformed or a coating is deposited onto a substrate. While the use of theplasma flame described by Hunt can produce nanocrystal powders forseveral metals and oxides, the method cannot be applied to production ofvitreous complex solid electrolytes or to produce layers with athickness below approximately 10 μm for most applications because theresulting films generally lack uniformity of thickness. Moreover, thedisclosed method can result in trapping foreign materials in the filmand partial oxidation of the material.

Some current vacuum methods include DC and RF magnetron sputtering,thermal sputtering and molecular beam deposition. The preferred methodgenerally depends on the desired chemical and physical properties of thematerial, the thickness of the film, and the deposition rate. Usingmolecular beam techniques, thin dense films from a broad group ofmaterials have been prepared. Films prepared by these procedures havebeen used in batteries. However, these methods are generallycharacterized by low deposition rates, the need for ultrahigh vacuum,and difficulty in obtaining RF sputtering targets and for deposition offilms having complex compositions.

Regarding batteries utilizing solid electrolytes, minimizing thethickness of solid electrolytes helps reduce the internal seriesresistance of the battery. However, although films of solid electrolyteshaving a thickness below 1 μm can be used to produce batteries havinglow internal resistance, internal short circuits (e.g. from Lidendrites) tend to develop, particularly when the films have largesurface areas. In practice films with a minimum thickness ofapproximately 10-20 μm are used because of technical difficulties inachieving a sufficient structural homogeneity to reduce the batterysize. Additionally, expense can be a concern due to the cost ofproviding certain conventional solid electrolyte materials.

Thus, lack of structural homogeneity can limit the use of available thinfilm sputtering processes for the production of thin films forbatteries. The methods are generally only suitable for production ofthin films for superionic conductors having simple stoichiometries. Formore complex films, the use of these techniques is generally furtherlimited by a low deposition rate.

Although vacuum thermal sputtering can generally provide up to a 1000fold increase in deposition rate compared to magnetron and molecularsputtering, thermal sputtering generally produces films having lowerdensity, degraded homogeneity and adhesion to substrates compared tothese related methods. The adhesion of the deposited layer to substratescan generally be improved by raising the temperature of the substrate,but can lead to structural changes in the deposited layer, such asincreased grain size.

The above limitations of thermal vacuum sputtering result mainly becausethe process is performed under high vacuum which results in low vapordensity and the process uses low energy sputtered particles (below 1eV). As a result, non-homogenous films are generally formed. Attempts toincrease film homogeneity by increasing reactor size, or by increasingthe evaporation temperature have been generally unsuccessful, as theylower the deposition efficiency and result in certain systeminefficiencies, such as requiring more frequent replacement of theevaporating device.

Accordingly, there is therefore a need for new methods of preparing thinfilms, particularly films having thicknesses of less than about 50 μm,that are efficiently deposited as homogenous layers substantially freeof foreign materials. The deposited layers should provide physical andchemical properties required for efficient function in batteries, fuelcells and other electronic active devices.

SUMMARY OF THE INVENTION

A method for depositing a thin film, includes providing a vaporincluding at least one selected vapor phase component into an evacuatedprocess chamber, condensing the vapor onto a heated substrate to form aliquid phase deposit, wherein a temperature of the substrate is lowerthan the condensation temperature of the component. To avoid solid phasedeposition occurring directly from the vapor, the substrate temperatureis preferably held at a temperature which is also higher than thesublimation temperature of the component, as defined herein. The liquiddeposit is then cooled to form a solid phase film.

As used herein, the term sublimation temperature refers to the maximumtemperature in which a solid phase deposit can directly result from thecorresponding vapor of the component. The condensation temperaturerefers to the maximum temperature of actual liquid phase formation fromthe vapor of the component. These respective values are related to thevalues determined experimentally under nonequilibrium conditions whichmay differ from the corresponding equilibrium values which may be shownin calculated phase diagrams.

The providing step can comprise evaporation. In this embodiment, theevaporating step can include utilizing a plurality of evaporationsources. The evaporation sources can be operated at differenttemperatures.

The substrate is preferably a metallic or ceramic substrate. The methodcan further include the step of cleaning the surface of the substratesurface prior to the providing step. The method also include the step ofholding a temperature of the process chamber above a sublimationtemperature of the component.

The method can include the step of varying the volume of the processchamber. The varying step can include reducing the process chambervolume prior to or during the condensing step. The varying step caninclude increasing the volume of the process chamber prior to or duringthe cooling step.

The method can comprise multi-step cycling. In this embodiment, only aportion of the thickness of the solid phase film is deposited in each ofa plurality of cycles, each cycle including providing, condensing andcooling steps. Some cycles can use at least one material chemicallydistinct from the component to produce multi-component materials havinga plurality of different layers.

The solid phase film can include a second layer disposed on a firstlayer, the first and second layers being chemically distinct. The firstlayer can be a cathode layer and the second layer can be a solidelectrolyte layer. The solid phase film can be a eutectic composition,the eutectic composition including a plurality of components.

The providing step can include melting a plurality of components to forma homogeneous material and evaporating the homogeneous material to forma solid phase eutectic film. The method can further include the step ofgrinding the homogeneous material prior to the evaporating step. Theplurality of components can also be stirred.

The cooling step can comprise active cooling or forced gaseous cooling.The method can include the step of introducing at least one additionalgaseous component into the process chamber during the evaporating step.

The solid phase film formed can be used as an electrolyte or anelectrode for a battery or for fuel cells and other electromagneticallyactive devices. The solid phase films can comprise oxides, borides,sulfides and fluorides.

BRIEF DESCRIPTION OF THE DRAWINGS

A fuller understanding of the present invention and the features andbenefits thereof will be accomplished upon review of the followingdetailed description together with the accompanying drawings, in which:

FIG. 1. illustrates a system for the deposition of thin films usingvapor condensation, according to an embodiment of the invention.

FIG. 2. illustrates a temperature profile for an evaporation device fordeposition of thin films using vapor condensation suitable for use withcertain electrolyte materials.

FIG. 3 illustrates the thermodynamic conditions for vapor condensationon substrates.

FIG. 4. illustrates the dependence of the specific electronicresistivity of a aluminum-solid electrolyte-stainless steel batterysystem on the level of defects in the electrolyte film.

FIG. 5. illustrates the structure of a film of the systemLi₂O—Li₂SO₄—B₂O₃ obtained according to the procedure described inExample 1.

FIG. 6. illustrates an X-ray analysis of the crystalline structure of athin film of the system Li₂O—Li₂SO₄—B₂O₃ obtained according to theprocedure described in Example 3.

FIG. 7. illustrates the film structure of the system Li₂O—Li₂SO₄—B₂O₃obtained according to the procedure described in Example 4.

FIG. 8. illustrates an X-ray analysis of the crystal structure of a thinfilm of the system Li₂O—Li₂SO₄—B₂O₃ obtained according to the proceduredescribed in Example 5.

FIG. 9. illustrates a SEM image of the surface of mechanically depositedpowder particles of (LiF)₂—Li₂WO₄—P₂O₅ described in Example 8.

FIG. 10. illustrates a film structure of (LiF)₂—Li₂WO₄—P₂O₅ deposited ona substrate using the crystalline powder described in Example 9.

FIG. 11. illustrates the temperature profile of an evaporation deviceduring MoO₃ powder evaporation.

FIG. 12. illustrates MoO₃ film structure obtained using a depositionaccording to the procedure described in Example 10.

FIG. 13. illustrates an X-ray diffraction analysis of a thin MoO₃ filmdeposited according to the procedure described in Example 11.

FIG. 14. illustrates a structure evidencing spalling of a MoO₃ filmdeposited according to the procedure described in Example 11.

FIG. 15. illustrates an X-ray diffraction analysis of a thin MoO₃ filmdeposited according to the procedure described in Example 12.

FIG. 16. illustrates a MoO₃ film not evidencing spalling depositedaccording to the procedure described in Example 12.

FIG. 17. illustrates the fine structure of MoO₃ film deposited accordingto the procedure described in Example 12.

FIG. 18. illustrates a temperature profile of an evaporation device forevaporation of a large amount of material according to the proceduredescribed in Example 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention substantially addresses deficiencies in current processesused for the deposition of thin films, particularly for thin filmshaving thicknesses of less than about 20 μm. The invention can providethin films having a high degree of homogeneity with respect to chemicalcomposition, structure and thickness. In addition, the invention canproduce films which adhere well to a variety of substrates. Theinvention can also provide a high deposition rate.

In one embodiment of the invention, a method for depositing a thin filmincludes the steps of providing a vapor including at least one selectedvapor phase component into a substantially evacuated processing chamber.The vapor is condensed onto a heated substrate to form a liquid phasedeposit by holding the temperature of the substrate lower than thecondensation temperature of the component, but higher than thesublimation temperature of the vapor phase component. As used herein,the term sublimation temperature refers to the maximum temperature inwhich a solid phase deposit can directly result from the correspondingvapor of the component. The liquid component is then cooled to form asolid phase film of the desired material.

Under the above conditions, the vapor material is deposited on thesubstrate not as a solid film, as in conventional thermal sputtering,but as a liquid film of substantially constant thickness, depending onthe wetability of the substrate surface. This ensures good adhesion tothe substrate, low porosity and uniform thickness of the deposit. Aftercooling, the liquid deposit solidifies.

The invention permits deposition of thin films without chemicallyaltering the source material. Although the invention can be used with asingle source material, the invention can provide two or more vaporphase components, such as co-evaporation of at least two reagent sourcesto form a plurality of vapor phase components, and condensation of thesame onto a substrate. The condensed reagent components can react in theliquid phase on the substrate surface following condensation. Thisprocess is shown in Example 14.

The invention is applicable to deposit a wide variety of layers,including thin films of metallic, semiconductor and nonmetallicinorganic materials. The invention is also useful for forming solidelectrolytes and electrodes for batteries. In addition, films formedusing the invention can be used for fuel cells and otherelectromagnetically active devices.

The invention requires that at least one vapor be provided in theprocess chamber. Evaporation of solid source materials can be used toprovide a vapor. For more complex desired compositions, such as theformation of eutectic electrolytes having a plurality of components,individual components in a suitable molar ratio in solid form can beplaced into a heating device, such as a furnace, for melting. The meltis preferably stirred. Stirring may be provided by a cavitationalstirring device. The liquid material can be dispensed onto a solidsurface and cooled to obtain particles having the desired eutecticcomposition. The particles can then be ground to a size preferably beingless than 100 μm to form a powder suitable for evaporation. Regardlessof the source of the vapor, the vapor is condensed on a heated substrateto form a liquid phase deposit by holding the temperature of thesubstrate at a temperature lower than the condensation temperature ofthe vapor phase component.

It is preferable to hold the process chamber walls at a temperaturesufficient to avoid deposition thereon, because deposition of evaporatedmaterial on the reactor chamber walls can lower the deposition rate onthe substrate and can lead to particulate inclusion in the depositedlayer. For example, flaking of films deposited on the process chamberwalls can result in particulate incorporation in the deposited film.Thus, respective temperatures of the process chamber and substrate arepreferably selected to condense liquid on the substrate, but not on theprocess chamber walls. For this purpose, the temperature of chamberswalls are maintained at a value above the condensation temperature ofthe vapor, while the substrate is maintained at a temperature below thecondensation temperature of the vapor.

The deposit spreads uniformly over the whole substrate surface under theinfluence of the surface tension of the deposited liquid. The depositedliquid is then cooled to form a substantially homogeneous solid thinfilm layer.

The resulting structure of the solid film formed depends on the coolingrate of the deposited liquid. Selected cooling rates depend on theparticular material as well as the intended use of the material. As thecooling rate increases, the structure of the deposited layer generallychanges from crystalline to microcrystalline (polycrystalline) toamorphous-crystalline to amorphous. The term amorphous-crystalline asused herein refers to a structure having localized small crystallitesdisposed in a substantially amorphous matrix.

Microcrystalline and amorphous-crystalline structures generally exhibita high degree of uniformity in chemical composition and also goodelectrochemical properties, such as ionic conductivity andelectrochemical activity. Electrochemical properties of films of cathodematerials based on molybdenum oxide, and solid electrolytes based oneutectic oxide and sulfide systems, have shown high values of cathodespecific energy and electrolyte conductivity when the films havemicrocrystalline and amorphous-crystalline structures, respectively. Theinvention can be used to deposit thick and multilayer films to provideelectrode and electrolyte materials for batteries including an electrodelayer disposed on an electrolyte layer.

FIG. 1 shows a system 100 adapted for depositing uniform thin filmsusing vapor condensation. System 100 can include a dosing device 110, aprocess chamber 120 having an adjustable working chamber volume and avalve 20 permitting isolation of the substrate from other parts of theworking chamber. A decrease in the volume of the working chamber duringthe evaporation/condensation process can increase the vapor density andthe rate of condensation of vapor on the substrate. After theevaporation/condensation process is complete, a subsequent volumeincrease of the working chamber with the valve closed can be used tolower the temperature of the deposited layer resulting from adiabaticexpansion, which can increase the rate of solidification of the film.

If evaporation is used to provide the vapor, cavitation stirring of themelt in the evaporation device can be used in combination with a systemfor correcting the composition of the vapor. For example, whenevaporating heavy and light elements together, the vapor compositionpreferably is corrected because of the different agility and partialpressure of the respective elements comprising the vapor. One or moreadditional evaporating or inlet gas systems can be used simultaneouslywith the main evaporator to supply additional vapor of one or morecomponents to raise the partial pressure of this component to correctthe composition of the vapor.

In some cases the electric resistance of the vapor depends on itscomposition. In this instance, it is possible to control the vaporcomposition “in situ” by measuring the electric current between twospecific electrodes under high (e.g. 500 V) voltage and correcting asdescribed above.

This method allows production of thin films of different materials onvarious substrates, such as metallic and ceramic substrates andsubstantially avoids segregation in the heater bath and providesformation of a high homogeneity vapor composition.

When the vacuum condensation method includes evaporation of at least onesolid source material, the resulting thickness, structural homogeneity,and resulting physical and chemical properties of the deposited filmhave been found to principally depend on the following parameters:

1. Temperature of the evaporation device;

2. Temperature of the vapor of the evaporated material;

3. Pressure and density of the evaporated material vapor;

4. Temperature and state of the substrate surface;

5. Rate of deposition of the condensed film;

6. Rate of cooling of the condensed film.

Other factors which can influence the process include the geometry andthe process chamber material, as well as the specific power density ofthe evaporation device. The influence of each of these parameters isconsidered separately, using an apparatus for the production of thinfilms using vapor condensation, such as the apparatus shown in FIG. 1.

Referring again to FIG. 1, desired film components are typicallyintroduced as a powder 3 inside a dosing device 110, which areintroduced into the process chamber 120 through a chute 4 using a dosingneedle 2. Dosing needle 2 can be controlled by an electromagnetic lever1.

The process chamber 120 is heated by a heating device 6, such asresistive heating elements, that can be protected by a shield 7. Aninert gas, such as argon, may be introduced through a pipe 5 which canbe directed to the side of the substrate 12. A second inlet for an inertgas through a pipe 8 can be provided for flowing an optional gas overthe deposited film. Preheated gas may also be introduced into thechamber through a pipe 21.

The substrate can be heated by a heater 11. The temperature of thesubstrate can be monitored by a thermocouple 13. A vacuum valve 20 isprovided to allow evacuation of the reactor chamber. An externalcompartment 15 of the process chamber is preferably expandable andcontractible to permit the volume of the process chamber to be modified.Evaporating device 17 can melt and evaporate one or more components tobe deposited.

The temperature profile of the evaporation device can be adjusted toensure a preliminary drying and outgassing of the source material. Withrising vapor density, the evaporation rate can decrease. This decreasecan be compensated by a corresponding temperature increase of theevaporation device. However, too sharp an increase of this temperatureat the beginning of the process may lead to formation of macroscopicdroplets. Macroscopic droplets generally show poor adhesion tosubstrates upon condensation on the substrate. However, macroscopicdroplets can be usefull when applied at the final step of the processsince these droplets are generally of an aerosol size and condensationon the already formed film can increase the specific area of the film.Increased specific film area can be useful in battery applicationsbecause it generally enhances the electrochemical properties of thecathode or solid electrolyte material.

A typical temperature profile for an evaporation device suitable forevaporating most eutectic oxide, sulfide and boride systems with amelting temperature in the range of approximately 900° C. to 1000° C. isshown in FIG. 2. The temperature profile shown in FIG. 2 includes 3stages. A first low temperature stage at 100-150° C. is a drying stage.An intermediate temperature stage at 900-1100° C. is an outgassingstage. The third stage, being at a temperature of up to 2000°, is whereevaporation occurs.

The temperature of the vapor determines the kinetic energy of the vaporatoms or molecules. The equation E=3/2 kT relating energy of a gas andtemperature should generally not be used to estimate the kinetic energyof the vapor atoms or molecules described herein as that equationgenerally applies well to an ideal gas, but not for a vapor. An increasein vapor temperature generally improves the adhesion of the resultingfilm to the substrate. However, assuming the reactor volume is heldconstant, increasing the temperature of the vapor during the evaporationstage influences its pressure and density. Generally, at a temperatureapproaching the critical temperature of the vapor in the vicinity ofsubstrate maximizes the deposition rate and provides a highlyhomogeneous film.

Vapor temperatures near the evaporator and substrate are generallysignificantly different. This is due to the high rate of evaporation ofan initial substance and a low thermal conductivity of the vapor.Because of the high rate of substance evaporation, pressure and vapordensity are also variable, but generally to a lesser extent thantemperature.

Thus, in the described system the vapor pressure, temperature and vapordensity are different in all parts of the system. Therefore, phasediagrams are not presented.

However, approximate consideration of the proposed invention can bepresented where the pressure and vapor density can be considered asconstants within a volume of the system. In this case, vaporcondensation without its solid phase deposition can be explained on thebasis of the schematic phase diagram shown in FIG. 3.

As shown in FIG. 3, at a constant pressure P_(o), the substance that isnear evaporator has higher temperature and is in a vapor state 310. Onthe other hand, near the substrate, where the substance is deposited,the temperature is lower. The phase corresponding the substratetemperature at pressure P_(o) is located in the region of a stableliquid phase 320. Thus, the invention provides vapor condensation on thesubstrate.

In the invention, vapour density and associated thermodynamic parametersare determined by the evaporation rate of the starting substance and therate of condensation on the substrate. In addition, initiation of vaporcondensation on a substrate occurs at a pressure which is generallyhigher as compared with its equilibrium value (located on a diagramline). This likely results because in passing to condensed state thevapor has to reach the necessary degree of supersaturation.

Independent temperature control systems are preferably provided forcontrol of the evaporator and substrate temperature. The temperaturecontrol systems are preferably computer regulated. Independenttemperature control systems for the evaporator and a substrate enablethe maintenance of a desired temperature distribution in a workingchamber substantially independent of the rate of spraying.

Wetting properties of several materials on a variety of substrates, suchas stainless steel (Cr₁₈Ni₁₀Ti) were investigated. It was found thatmost eutectic cathode oxide electrode materials are deposited onstainless steel (Cr₁₈Ni₁₀Ti) as a liquid film rather than discretedroplets, the thickness of which depends on the viscosity and thesurface tension of the liquid at the selected substrate temperature.

Following liquid deposition, forced cooling may be used to more quicklysolidify the liquid. For example, a jet of an inert gas may be used tocool the liquid deposited. The structure of the solid that is formedgenerally depends on the cooling rate. As the cooling rate increases,the degree of crystallinity generally decreases.

For electrode and solid electrolyte materials used in batteries, such asoxides of Mo, W, Li, B, and their eutectic compositions, at coolingrates of up to 2 K/s a crystalline structure is generally formed. Anincrease in the cooling rate to approximately 5 to 7 K/s generally leadsto the formation of a eutectic fine-grained structure. A furtherincrease of the cooling rate in eutectic systems of solid electrolytesleads to the formation of an amorphous-crystalline structure and amicrocrystalline or mostly amorphous structure in the case of electrodematerials. An amorphous-crystalline structure consists of highlydispersed crystalline phases with a broad homogeneous amorphous domain,and allows different kinds of solid solutions therein.

The invention can be used to form a thin film structure that differsfrom the structure of the initial source material. For example, for thedeposition of solid electrolytes for batteries, the initial materialsare generally eutectic compositions having a melting temperature in therange 800-1000° C. Using the invention, a condensed thin liquid film isinitially formed which subsequently solidifies under controlled cooling.Controlled cooling can be provided by forced gas, such as an argon jet.The substrate temperature and the cooling rate are chosen in such amanner that an amorphous-crystalline structure is formed having anenhanced ionic conductivity at room temperature.

Such a structure can provide for a 500-1000 fold increase of the ionicconductivity of the electrolyte, which is believed to result from theformation of vacancies on the interfaces between the insertedcrystalline phases in an amorphous matrix. An inserted phase increasingthe conductivity of solid electrolytes has been reported in severalinvestigations regarding mechanical mixtures of aluminum and siliconoxides and halogenides of lithium, silver and copper (Wagner Jr., J. B.in: C.A.C. Sequeira and A. Hooper, Sequeira and A. Hooper, Solid StateBatteries, Matinus Nijhoff Publ. Dordrecht, 1985, p. 77). The inventioncan enhance this effect because of the minimization of micropores andother macrodefects. In addition, additional ion transfer along vacanciesbetween the most closely packed faces of the crystal lattice can furtherenhance this effect.

Additional ion transfer is achieved primarily as a result of vacanciescreated in the solid electrolyte. It is known that rising temperatureincreases the equilibrium concentration of vacancies. During forcedcooling of thin films by a jet of a cooling gas, some of the vacanciesare not annihilated and remain in the final film. This generally has apositive effect on the ionic conductivity of the electrolyte film.

The cooling process can be adjusted based on desired film properties. Inthe case of forced gaseous cooling (e.g. Ar) to achieve thick layers, agas can be directed toward the side of the substrate. This can preventthermal cracking of the film. When a desired thin film requires a highcooling rate for formation of an amorphous-crystalline structure, thecooling jet can be directed to the side of the deposited film. When highthermal stresses are known to develop, the jet can be directed from bothsides of the deposited film.

To reduce the time required for deposition, the deposition rate may beincreased by decreasing the volume of the process chamber. The decreasedprocess chamber volume increases the density of the vapor, which canincrease the deposition rate.

A multilayer deposition of the same or different materials may beachieved by using a cyclic multistep process. For example, anevaporation device can be filled with the desired source material, thesource material evaporated and the resulting vapor condensed on asubstrate. The substrate can then be cooled at a rate 0.1 to 100 K/s tosolidify the film. The process chamber can then be evacuated. Theevaporating device can then be refilled with the same or a differentsource material, and the steps repeated. Alternatively, if multipleevaporating devices are provided, the refilling step would not berequired.

Using a cyclic procedure, relatively thick films (e.g. >20 μm) can beproduced which retain their microcrystalline or amorphous-crystallinestructure compared to the one step evaporation, when a substantiallycrystalline structure often results from non-optimum cooling. Relativelythick films can be produced which retain their microcrystalline oramorphous-crystalline using the cyclic procedure, where only a thinlayer is rapidly cooled during each cycle.

There are generally substantial difficulties in effectively coolingrelatively thick films (e.g. >20 μm), obtained by a one step evaporationmethod, where cooling follows deposition of substantially the entirelayer thickness. Because of low thermal conductivity of many materials,including most electrolyte and electrode materials, the cooling ratenecessary for amorphous-crystalline structure formation is obtained onlyfor a thin outer surface layer of the film. Inside the film, heatremoval is less efficient and as a result, a crystalline (e.g.polycrystalline) structure generally forms throughout the material.During the multilayer cyclic deposition process, a plurality of coolingand deposition steps are used, cooling occurring after each thin layerdeposition. As a result, cooling is much more efficient as compared toconventional cooling processes.

The vapor condensation followed by cooling produces composite filmstacks (e.g. cathode/solid electrolyte) with good adhesion between therespective layers. Good intra-layer adhesion as well as inter-layeradhesion also results when interval deposition is used for one or morelayers.

If a large amount of material is to be deposited using evaporation froma melt (see Example 15), it is recommended to cavitationally stir themelt, such as by using an ultrasound magnetostriction device to coupleultrasound radiation to facilitate evaporation of the material. In theexperiments performed a frequency of 22 KHz was used.

Melt stirring can be helpful because the evaporation process takes placemostly from the surface of the melt. In the case of large amount of thematerial to be evaporated, convection in the liquid does not havesufficient time to compensate the lack of the component with the highestevaporating rate being on the surface of the melt.

For the deposition of complex multi-component electrode and electrolytematerials, if the components have low reciprocal solubility in the solidstate, separate evaporation devices for each component with differentevaporation temperatures are preferably used. For cyclic depositions, anadiabatic compression or expansion of the process chamber may be usedduring the deposition and cooling steps, respectively, in order toaccelerate the procedure and to enhance heat transfer from the depositedfilm.

The adhesion of thin films deposited using the invention generallydepends on the state of the specific substrate surface. The adhesion maybe enhanced by adding a preliminary cleaning of the substrate surfaceprior to deposition. For example, solution cleans, ion beam and plasmatreatments known in the art may be used.

A pulse deposition may be used in some cases, to produce thin films withimproved surface smoothness. A pulse deposition deposits a portion ofthe desired layer thickness, suspends the deposition process for aperiod, and then deposits another layer portion. A pulsed deposition canbe realized using a shutter that can isolate the evaporated vapor fromthe process chamber. For example, the shutter can be opened for a shorttime when the vapor reaches a predetermined temperature and the walls ofthe process chamber and the substrate reach the desired temperature. Ifthe shutter is reasonably hermetic, the pressure increases near theheater. As a result, the flow of the depositing material becomesoriented towards the substrate.

In some applications it may be desirable to add components into the filmwhich are not present, or are present only in small quantities in theinitial source material (see Example 7). In this case, one or more gasescan be introduced into the process chamber during deposition whichcontains the desired additional component before cooling the substrate.The gas is preferably preheated to a desired temperature, such as thetemperature of the reactor chamber.

A thin additional metallic layer such as Cu, Au, Pt, Al, Al—Li alloy orLi layer having a thickness of up to approximately 5 μm may be depositedon the surface of the deposited thin film. This layer can be used fordetermining properties of the layer formed from the vapor condensationprocess. For this purpose, the specific electrical resistivity(expressed in units of ohm-cm) between the substrate and the additionalmetallic layer can be measured through the film formed from the vaporcondensation process. If the resistance value measured is lower than thevalue calculated from the specific conductivity and the geometricdimensions of the film, the presence of a film having high porosityand/or the presence of a high concentrations of defects may be indicated(see FIG. 4). Lower specific electrical resistance using the inventionis believed to result because of good adhesion to solid electrolytes andcathode materials and because the deposited metals penetrate in porousmicro cracks and other defects of the film. This reduces local shortcircuits and generally decreases the specific electric resistance of thefilm.

EXAMPLES

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those having skill in theart that the methods and procedures disclosed in the examples whichfollow represent methods discovered by the inventors to function well inthe practice of the invention, and thus can be considered to constitutepossible modes for its practice. However, those of skill in the artshould appreciate that many changes can be made in the specificembodiments which are disclosed and still obtain a like or similarresult without departing from the spirit and scope of the invention.

Example 1 High Vacuum Evaporation on a Substrate Held at RoomTemperature

Vitreous electrolyte of the system Li₂O—Li₂SO₄—B₂O₃ at a component ratioof 0.5-0.15-1 moles, respectively, in a quantity of 40 g was melted in amuffle furnace in an environment of flowing argon. After completemelting of the components at temperature 950° C., the melt was subjectedto ultrasonic cavitational stirring at 22 kHz frequency for 5 minutes.Pouring was carried out on a surface of rotating rolls to obtain ahomogeneous material. After pouring through the rotating rolls thesolidified material forms thin flake-like particles with scales(cracked) edges. The material was then ground mechanically up tofractions less 100 μm for spraying.

Powder weight, with a mass of 40 mg was placed in the 5 cm³volume-chamber preliminary pumped out to a high vacuum of about 10⁻⁶torr, and was evaporated using a tungsten pipe heater under thetemperature conditions shown in FIG. 2.

Spraying was carried out on a stainless steel substrate at roomtemperature. A thin film with the following parameters was obtained:

Thickness—4 μm,

Variation in thickness ±1.8 μm,

Number of defects (discontinuities) determined using quantitativemetallography—18%,

Amorphous structure.

A large number of defects (FIG. 5) which indicate poor adhesion to asubstrate and significant variation in thickness of the film did notallow determination of conductivity. This indicates application of thefilm formed for batteries would generally not be practical.

Example 2 Chamber Wall Temperature

Conditions described in Example 1 were again used, except thetemperature of chamber walls was increased up to 600° C. A thin filmhaving the following parameters has been obtained:

Thickness—8 μm,

Variation in thickness ±0.2 μm,

Number of defects (discontinuities) determined using quantitativemetallography—12.6%,

Amorphous structure.

The higher chamber wall temperature increased the deposition efficiency.However, the conditions used did not significantly increase in filmquality and adhesion to a substrate.

Example 3 Substrate Temperature

Conditions described in Example 2 were again used, except thetemperature of a substrate was changed to 300° C., and the rate of filmcooling after spraying was 25K/min. A thin film having the followingparameters was obtained:

thickness—8 μm,

variation in thickness ±0.2 μm,

number of defects (discontinuities) determined using quantitativemetallography—0.6%,

crystalline structure (FIG. 6) with grain size up to 50 μm.

The increase in substrate temperature did not change the depositionefficiency. However, the higher substrate temperature allowed asignificant increase in the quality of the film and its adhesion to asubstrate. The coarse-crystalline structure of the resulting film alsolimited its ionic conductivity to being about 1.1×10⁻⁶ S·cm⁻¹.

Example 4 Substrate Cooling Rate

Conditions described in Example 3 were again used, except the rate offilm cooling after spraying was increased to 150K/min. A thin film withthe following parameters was obtained:

Thickness—7.2 μm

Variation in thickness ±0.2 μm

Number of defects (discontinuities) according to the data ofquantitative metallography—0.3%

Fine dispersion crystalline structures with the average grain size 8 μm(FIG. 7).

Increasing the rate of film cooling as compared with Example 3 did notsignificantly changed the efficiency of material deposition, filmquality and its adhesion to a substrate. However, the increased filmcooling rate has resulted in an increase in crystalline phasedispersion.

Example 5 Substrate Cooling Rate

Conditions described in Example 4 were again used, except the rate offilm cooling after spraying was increased up to 350K/min. As a result,thin film with the following parameters has been obtained:

Thickness—7.5 μm,

Variation in thickness ±0.2 μm,

Number of defects (discontinuities) determined using quantitativemetallography—0.4%,

Amorphous-crystalline structure (FIG. 8).

Increasing the rate of film cooling did not significantly change theefficiency of the material deposition, film quality, and its adhesion tothe substrate. However, the higher substrate cooling rate produced anamorphous-crystalline structure which resulted in an improvement inionic conductivity, reaching a level of 4.6×10⁻⁴ S·cm⁻¹.

Example 6 Substrate Temperature and Vapor Density Optimization

Deposited material: Li₂O—Li₂SO₄—B₂O₃

Deposition Parameters:

Temperature profile of evaporating device: as indicated in FIG. 2

Amount of the used material: 140 mg

Deposition duration: 40 s (non cyclic)

Vapor density: 60 kg/m³

Temperature of reactor chamber: 600° C.

Temperature of substrate: 250° C.

Parameters of the Deposited Film

Thickness of the deposited film: 6μ

Thickness nonuniformity: 4%

Ionic conductivity (from impedance measurements): 2.0×10⁻³ S·cm⁻¹

Substrate diameter: 20 mm

Substrate material: stainless steel Cr₁₈Ni₁₀Ti after cleaning with aionic beam.

Structure: amorphous-crystalline (see FIG. 8)

Electronic resistance at room temperature (between the substrate andadditional deposited Al film) 22 kΩ

Simultaneously optimization of substrate temperature and vapor densityresulted in increasing the ionic conductivity of the film withoutsubstantially changing the uniformity in composition and thickness.

Example 7 Cycling Evaporation

Deposited material: (LiF)₂—Li₂WO₄—P₂O₅

Deposition Parameters:

Temperature profile of evaporating device: as indicated in FIG. 2

Regime of evaporation: two cycle (cycle duration—70 s.)

Amount of used material: 120 mg per one cycle

Maximum vapor density: 80 kg/m³

Temperature of reactor chamber: 600° C.

Temperature of substrate: 250° C.

Chamber volume decreasing during evaporation, and increasing duringcooling—by a factor of 2.2 times

Cooling procedure: argon jet from both sides

Parameters of the Deposited Film:

Thickness of the deposited film: 16 μm

Thickness nonuniformity: less than 5%

Ionic conductivity (from impedance measurements): 2.6×10⁻⁴ S·cm⁻¹

Substrate diameter: 20 mm

Substrate material: stainless steel Cr₁₈Ni₁₀Ti after cleaning with aionic beam.

Structure: amorphous-crystalline (see FIG. 8)

Electronic resistance at room temperature (between the substrate andadditional deposited Al film: 45 kΩ.

Example 8 Liquid Phase Formation on the Substrate

Solid electrolyte of the (LiF)₂—Li₂WO₄—P₂O₅ system obtained by themethod described in Example 1 was ground up into fractions less than 20μm and were applied in a dry manner to a stainless steel substrate. Theparticles were fixed on the substrate surface using compression of about100 kg/sm². Small (up to 7-9 μm) particles of fragmental forms wereconfined by surface tension forces and had sufficient adhesion to asubstrate. The structure of a surface having the mechanically depositedpowder particles thereon is shown in the scanning electron micrograph ofFIG. 9.

Example 9 Cycling Evaporation of Powder

The material having the same composition as the powder applied in themethod of Example 8 was evaporated onto the substrate obtained by themethod described in Example 7.

The analysis of structure of the obtained film (FIG. 10) was obtained bythe methods of optical and scanning electron microscopy. This exampleshowed that small fragmental particles dissolved in the evaporated layerwhile larger particles had modified their shape from fragmental form toround one. Such structural modifications can be explained only due toformation of liquid phase on a surface of a substrate. This liquid phasehardens during subsequent cooling.

Example 10 High Vacuum Evaporation of MoO₃ Cathode Material

Chemically pure powder MoO₃ was sprayed after 30 seconds drying at 100°C. in a closed volume under the temperature conditions shown in FIG. 11at vapor density 40 kg/m³ in a vacuum with residual pressure of 10⁻⁶torr. The evaporation was onto a stainless steel substrate held at atemperature of 100° C. The temperature of the working area was 650° C.

The thin (5 μm) film obtained had a considerable number of exfoliationsections from the substrate (up to 20%, see FIG. 12), that preventedresulting electrochemical characteristics to be determined.

X-ray analysis revealed a small amount of an amorphous component andoxide phases, such as Mo₉O₁₁. The composition obtained is not generallysuitable for electrochemical applications because of larger deviation ofphase composition from that of terminal oxide (MoO₃).

Example 11 Oxygen Added During Evaporation Substrate and Walls ChamberTemperature Optimization, One Sided Cooling of Substrate

Evaporation was made under the conditions described in Example 10,except an oxygen pressure of 0.05 torr was established in the chamber,the substrate temperature was increased to 250° C. and the temperatureof working space set to 650° C. After evaporation the chamber was cooledby cold argon of high purity with the rate 4 K/sec directed at the sideof the film.

As a result, a thin film with the following parameters has beenobtained:

Thickness—7.5 μm,

Variation in thickness ±0.4 μm,

Number of defects (discontinuities) determined using quantitativemetallography—8.8%,

A generally amorphous structure resulted having crystal phases Mo₉O₂₆and Mo₄O₁₁ of no more than 6-7% (see FIG. 13). However, analysis byoptical microscopy revealed considerable film spalling (FIG. 14), thatnegatively influenced the resulting galvanostatic characteristics shownbelow.

Galvanostatic Characteristics

Substrates with the thin layer of the above described cathode materialof known weight were placed in a standard element 2325. One molar LiClO₄in a mixture of propylene carbonate solvents and dimethoxyethane in aratio of 3 to 1 was used as the electrolyte. A lithium anode andmicroporous polypropylene separator were also provided. Charge-dischargecell characteristics were investigated using an automatic cycling standwith computer control. Cycling range of the system was 1.1-3.5 V,discharge current −25 μA/cm², charging current was 12.5 μA/cm².

The specific capacity of the cathode material was determined to be 50mA·h/gr (14% of theoretical), having no ability for reversible work.

Example 12 Both Inner and Outside Cooling of the Substrate

Spraying was carried out under the conditions described in Example 11.However cooling was directed to both the substrate and the film.

As a result, thin film with the following parameters were obtained:

Thickness—6.0 μm,

Variation in thickness ±0.4 μm,

Number of defects (discontinuities) according to the data ofquantitative metallography—0.4%,

Rate of film cooling—3 K/s,

Amorphous structure with the contents of crystal phase Mo₉O₂₆ of no morethan 7-8% (FIG. 15). Film spalling was not found in an analysis byoptical microscopy performed (FIG. 16). Detailed analyses of thecrystalline phase by the method of scanning electron microscopy (FIG.17) revealed the crystallites were dispersed, less than 25-40 nm inthickness, and showed a plate-like morphology (FIG. 17).

The method described in this example provided improved galvanostaticcharacteristics as determined by the technique described in Example 11.Resulting galvanostatic characteristics included a specific capacity ofa cathode material of 270 mA·h/gr, (75% of theoretical), and reversiblework ability. These characteristics are considered satisfactory forelectrochemical applications.

Example 13 Multi-Layer (Cathode—Solid Electrolyte) Thin Films

In this example, a Li₂O—Li₂SO₄—B₂O₃ electrolyte was evaporated onto aMoO₃ cathode. Spraying was performed under the conditions described inExample 12, except solid electrolyte of the Li₂O—Li₂SO₄—B₂O₃ system at acomponent ratio of 0.5-0.15 -1 moles was evaporated onto the surfaceMoO₃ under the conditions of Example 6. Morphological and structuralcharacteristics of the films of the cathode and electrolyte materialscorresponded to Example 12 and 6, respectively.

Resulting Parameters of the Films:

Total conductance of the electrolyte (from impedance measurements):2.9×10⁻⁴ S·cm⁻¹

Diameter of the substrate: 20 mm

Structure of the electrolyte: amorphous-crystalline

Structure of the cathode: amorphous containing not more than 8% ofcrystalline phases of the type Mo₉O₂₆.

Measurement of the galvanostatic characteristics by the method ofExample 12 showed that the specific capacity of the cathode material was330 mA·h/gr (92% of theoretical), with capability to reversible work.These characteristics are considered satisfactory for electrochemicalapplications.

Example 14 Process and Condition of Co-Evaporation

Thin film from the material and by the process desribed in Example 4 wasobtained, except 10 mg B₂O₃ was sprayed from additional evaporatorsimultaneously with evaporation the main electrolyte componentLi₂O—Li₂SO₄—B₂O₃. The evaporation of B₂O₃ was performed according thetemperature regime shown in FIG. 2, except the outgassing stagetemperature used was 500° C.

An amorphous-crystalline structure shown in FIG. 8 was substantiallyobtained. This resulting structural characteristic produces electrolyteshaving improved ionic conductivity (see Example 5).

Example 15 A Large Amount of Material for Evaporation Aided byUltrasound Stirring

A (LiF)₂—Li₂WO₄—P₂O₅ film with the thickness 18 μm was obtained usingthe Example 1 process conditions and apparatus, except as noted below.

The amount of the material for evaporation was 300 mg. The time ofevaporation was increased to 150 seconds (FIG. 18).

Microprobe analyses revealed the concentration of W in the film comparedwith the concentration in initial solid material.

The experiment was repeated without changing conditions, but the melt inthe heater was stirred using an ultrasound magnetostriction deviceoperated at a frequency of 22 KHz. The difference in W concentrationbetween the evaporation source material and the solid layer formed fromvapor condensation was less than 1.0%, as shown in following tablebelow: Material % W Initial (LiF)₂—Li₂WO₄—P₂O₅ powder 61.2 Filmdeposited without stirring 44.0 Film deposited with stirring 60.3

While the preferred embodiments of the invention have been illustratedand described, it will be clear that the invention is not so limited.Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as described in theclaims.

1-23. (canceled)
 24. An apparatus for depositing a thin film fordepositing uniform thin films using vapor condensation comprising: adosage device; a substrate holding device for holding a substrate as thethin film is deposited thereon; and a process chamber exposed to thesubstrate and having a pair of members telescopingly engaged with oneanother and movable cyclically and adiabatically with respect to oneanother thereby increasing and decreasing the volume of said processchamber to increase the density of the vapor as said members arecontracted relative one and the other.
 25. An apparatus as set forth inclaim 24 wherein by said members expand and contract relative one andthe other for increasing and decreasing the volume of said processchamber as the thin film is deposited on the substrate.
 26. An apparatusas set forth in claim 24 including wherein said dosage device holds apowder and a chute with a needle through which the powder is introducedinto said process chamber.
 27. An apparatus as set forth in claim 24including an electromagnetic lever for controlling said dosing needle.28. An apparatus as set forth in claim 24 including a heating device forheating said process chamber with said heating device having resistiveheating elements, and a shield for protecting said resistive heatingelements.
 29. An apparatus as set forth in claim 24 including a pipeexposed to said substrate holding device for introducing a inert gasdirected to the side of the substrate.
 30. An apparatus as set forth inclaim 24 including a second inlet exposed into said process chamber forintroducing the inert gas through a pipe over the deposited thin film.31. An apparatus as set forth in claim 24 including a third pipe forintroducing preheated gas into said process chamber.
 32. An apparatus asset forth in claim 24 including a thermocouple for monitoringtemperature of the substrate.
 33. An apparatus having a dosage devicefor depositing a thin film for depositing uniform thin films using vaporcondensation, said apparatus comprising: a substrate holding device forholding a substrate as the thin film is deposited thereon; and a processchamber exposed to the substrate and having a pair of memberstelescopingly engaged with one another and movable cyclically andadiabatically with respect to one another thereby increasing anddecreasing the volume of said process chamber to increase the density ofthe vapor as said members are contracted relative one and the other.